We have cloned extensive DNA sequences from four Drosophila heat shock loci, 63BC, 87A, 87C, and 95D. The 63BC and 95D loci code for the 83,000 and 68,000 dalton heat shock proteins, respectively. At 87A and 87C there are closely homologous sequences coding for the 70,000 dalton heat shock protein. Also at 87C there is a 1.5 kb repeated sequence which is transcribed in response to heat shock but which does not code for protein. We are using various heat shock clones to study sequence organization, transcription, processing, and regulation of heat shock genes. We are also studying the transposition behavior and sequence organization of cloned dispersed repetitive elements, including the above mentioned 1.5 kb sequence, in D. melanogaster and its sibling species D. simulans and D. mauritiana.